# Idempotency

> The Idempotency-Key header: a retried request does not create a second task or charge twice.

```http
Idempotency-Key: order-1001
```

Pass a unique value (order ID or UUID, up to 128 chars) to `createTask`.

| Situation | Result |
|---|---|
| Retry with the same key and body | Same `taskId`, `idempotentReplay: true`, no charge |
| Same key, different body | `409 idempotency_conflict` |